The present invention concerns the construction of an expanding winding head that is particularly suitable for winding paper tape into rolls.
Winding heads with expanding elements for winding paper tape into rolls are already known in the art. The heads of their expanding elements are inserted into a tubular centre ends around which the paper is wound and the winding heads are connected to a drive shaft that rotates them thus winding the paper tape around the tubular centre and forming a roll.
One type of pneumatic expanding winding head of a known type consists of an essentially cylinder shaped external body with an internal cylindrical chamber in which there is a compressed-air operated piston whose rod runs axially inside a tubular spindle that is rigidly connected to the external body. The end of the tubular centre around which the paper is wound is caused to adhere to the tubular spindle by the radial force applied by sectors with grooved external surface against its internal surface of the spindle, which are externally coaxial with the tubular spindle. These sectors are moved by splines that are themselves radially moved when the piston is moved in an axial direction.
The degree of gripping between the tubular centre on which paper is wound and the sectors with a grooved external surface coaxial with the tubular spindle, depends on the extension of the surfaces which are in mutual contact, and increases the further the aforementioned surfaces are extended.
When the internal diameter of the tubular centre on which paper is wound and the external diameter of the tubular spindle with the sectors as above are of a considerable size, a sufficiently high degree of adherence is obtained so that, when the expanding spindle is rotated, the tubular centre is also rotated without slipping against the grooved sections. When the aforementioned diameters are below a certain minimum size, the size of the surfaces in mutual contact is also reduced and the degree of force with which these surfaces are pressed together is also reduced because the diameter of the piston running axially inside the external body of the winding head is diminished. In this case, due to the reduction both in the size of the surfaces in mutual contact and the pressure with which these surfaces are pressed together, there may be a degree of slipping between the two surfaces during rotation as it cannot be ensured that the tubular centre grips the tubular spindle.
This is one of the limitations of the pneumatic expanding spindles of a known type described above, as some manufacturers of paper rolls use tubular centres with a small diameter.
It should be pointed out that the external diameter of the external body of the winding head cannot be larger than the external diameter of the tubular centre on which the roll is wound; in fact, during the initial stages of winding, the paper type is caused to adhere to the tubular centre by a pressure roller belonging to the machine producing the tape, that glues the end of the tape to the tubular centre. During winding, this roller remains in contact with the roll and keeps it compact. It can thus be seen that if the external diameter of the tubular centre were smaller than the external diameter of the external body of the expanding winding head, the pressure roller used in the initial stages of winding would be prevented from touching the tubular centre.